- cleanup of the virtual function definitions for inventory items. Let's better use 'virtual' and 'override' everywhere to make sure that nothing gets overlooked.

- added call wrappers and script hooks for all relevant virtuals in AInventory.
- made GetSpeedFactor and GetNoTeleportFreeze entirely scripted because they are too trivial - also do them iteratively, just like HandlePickup, because it's just a better way to do this stuff.

src/g_inventory/a_weaponpiece.cpp

@@ -103,7 +103,7 @@ void AWeaponPiece::Serialize(FSerializer &arc)
 bool AWeaponPiece::TryPickupRestricted (AActor *&toucher)
 {
 	// Wrong class, but try to pick up for ammo
-	if (ShouldStay())
+	if (CallShouldStay())
 	{ // Can't pick up weapons for other classes in coop netplay
 		return false;
 	}